The invention relates to a multifiber fiberoptic coupler.
In general, fiberoptic couplers are created for the purpose of splitting the optical power in an optical fiber to two or more optical fibers or, conversely, to couple optical power present in two or more optical fibers into an optical fiber.
As described in earlier publications that are too numerous to be described individually, the fiberoptic couplers are made either by fusing or by bonding two or more optical fibers in a coupling region. The key to a successful coupler fabrication is a good control over the placement of the fibers brought into contact with each other in the coupling region prior to the fusion or bonding. For example, in the fusion process, imperfections such as insufficient contact between the fibers, dirt on the fiber surfaces, imbalances in tension forces applied to the fibers prior to the application of fusion heat, and three-dimensional non-uniformities in the applied heat could result in a low fabrication yield of couplers.
Fiberoptic couplers have been previously fabricated using two, three, or more bonded or fused optical fibers. The geometrical considerations attained in the coupling region substantially govern the coupling ratio between the individual optical fibers of the fiberoptic couplers; this is particularly true for couplers formed by identical optical fibers.
A simple known approach to fabricating a coupler is fusing two optical fibers to create a 2.times.2 coupler. If fiberoptic couplers of more than two optical fibers are needed, they are frequently fabricated by combining several 1.times.2 couplers in a tree or star like formation. However, this type of formation is not only fragile due to the vulnerability of the interconnecting fibers between the couplers but also bulky; this creates some difficulties in packaging.
Fused couplers have been made from seven identical optical fibers, wherein six fibers are arranged around a seventh inner fiber. In this geometry, the six outer optical fibers can be arrayed in perfect symmetry around an identical central optical fiber so that each of the surrounding fibers will contact both of its neighboring fibers and the central fiber in the same manner. Such perfect symmetry is not possible with other numbers of identical fibers.
Another prior approach to aligning and maintaining reliable contact among fibers prior to and during the fusion employs using a surrounding structure such as a tube made of an optical material. It is necessary to treat the surrounding tube on the optical fibers and the entire assembly is then heated and drawn in the fuse-drawing process. In some arrangements, it is difficult to maintain the threaded fibers precisely aligned prior and during the fusion process.
Couplers using less than seven identical optical fibers have been difficult to make since it is relatively difficult to obtain a periodic spacing and a uniform contact of the surrounding fibers. This is a disadvantage because many fiberoptic power distribution systems require equal power splitting in multiples of four optical fibers.
Thus, there is a need for a multifiber coupler design that is easy to fabricate, has a high fabrication yield and can accommodate a variable number of identical optical fibers with selected power distribution.